The circuit components and modules for various electronic systems, such as, for example, telecommunication systems and equipment, are often arranged and housed in the form of one or more printed circuit boards. The multiple electronic components or modules are mounted on the board, and conductive traces or patterns operably connect the components together. For example, the motherboard of an RF power amplifier, as used in telecommunication applications, will contain not only individual circuit components, but also must support one or more larger power converter modules for various power requirements on the motherboard. One particular constraint in system design and manufacturing of such boards is the amount of space that each board has to handle the various components and modules. Additionally, a simpler mechanical/physical design is realized when the power module is mounted to the bottom side (versus top side) since it is easier to mate to a heat sink (for purposes of necessary heat dissipation from the power module).
To maximize the amount of available surface area of a printed circuit board on the top component side of the board, or to address certain mechanical design constraints that are due to product size requirements, various larger circuit components are often attached to the bottom side of the circuit board. For example, the power converter modules for a system are often mounted on the bottom side. In that arrangement, the through-hole leads or pins for the power converter module protrude from the bottom of the board up to the top side of the board. This arrangement often leads to difficulties and inefficiencies in board fabrication and manufacturing and thus can lead to higher costs.
Specifically, the primary existing method to connect bottom side power converter module leads to a circuit board is by manual/hand soldering. FIG. 1 illustrates a circuit board 10, with a bottom side power converter module 12, coupled thereto by soldering 13. The hand soldering is very difficult due to the large mass presented by the leads 14 of the power converter module 12, as well as the extensive external and internal power planes that typically exist on the circuit board 10. For example, there may be as many as 16 leads that require hand soldering for a “full brick” power converter module 12. Special automated methods of solder attachment are also available for bottom side power converter attachment, including robotic soldering and selective wave machines. However, these machines are not standard equipment items in board manufacturing shops and rework/repair facilities, are very high capital expense items, and still experience similar solder difficulties as manual soldering due to the large mass of leads and extensive power planes on the circuit board.
This problem is further compounded by the fact that the power converter module has internal solder connections that are at risk of solder re-reflow, and subsequent damage, when the external leads 14 are manually soldered to the circuit board. As a result, the risk of internal damage requires each power converter module manufacturer to stipulate strict manual solder parameters (e.g., temperature and solder iron dwell time applied to each lead). Such parameters are extremely difficult to adhere to.
Still further, the recent introduction of lead-free solder alloys (RoHS regulations) results in still greater difficulty with manual soldering. This is because lead-free solders have much higher melting temperatures than traditional lead-based alloys and thus do not “wet” as easily. Furthermore, the periodic need to remove a soldered power converter module (such as for rework or repair) is extremely difficult, and often results in irreparable damage to the circuit board and/or the module.
Consequently, a socket interconnect approach is desirable as a means of coupling the power converter module to and from the circuit board assembly without the need for manual or special automated soldering.
However, the existing and commercially available through-hole socket arrangements and components have significant drawbacks. For example, various off-the-shelf power sockets are configured for a “top-entry” design. Therefore, for components, such as the power converter modules 12, that are mounted to the bottom side (as shown in FIG. 1) the socket must also be attached to the bottom side of the circuit board 10. This bottom side manufacturing scenario always requires special assembly processes for the attachment of the socket to the circuit board. Therefore, hand soldering is necessary. Alternatively, an extra pass through the reflow oven might be required. Such extra assembly processes or manual processes inevitably result in higher assembly costs and/or inferior attachment quality (including inferior long-term reliability) of the components or modules to the board.
A further complication is that many commercially available off-the-shelf power sockets that have a discrete design are not suitable for the vacuum pickup that is used in automated pick-and-place techniques using standard surface-mount assembly equipment. Therefore, the power sockets require either special assembly processes or hand placement. A special assembly process requires special automated insertion equipment, such as odd-form placement equipment, with grippers. This results in additional capital costs. Hand placement, on the other hand, is inferior in both cost and quality, as compared to viable automated placement alternatives.
Existing, discrete power sockets also have very stringent positional tolerance requirements in order to mate properly with a multi-pin power converter module. Such tolerance requirements mandate a circuit board with a physical design that has very tight mounting hole clearances. The tolerance requirements make it infeasible to use automated insertion techniques with standard assembly equipment. This further dictates that manual placement be used, resulting in higher assembly costs. Additionally, the reliability of the solder joint is compromised, per electronics industry end point requirements, because the tight clearance between the socket and board hole does not provide sufficient space for the proper flow of solder. These sockets do not have ability to properly mate and provide proper contact force for pins of power converters which have high positional tolerance.
Non-discrete power sockets, which may include a “ganged” design of discrete sockets, utilize a plastic, molded carrier to simultaneously insert all sockets. The ganged design permits the use of standard automated surface-mounting equipment. However, such sockets are still a top entry design. Therefore, they also require bottom side attachment and hand soldering, or an extra pass through the reflow oven, as noted above. Additionally, this ganged approach is cost prohibitive for small to moderate volumes of different power converter module designs that have different pin arrangements. This is because hard tooling is required for the plastic carrier, and separate inventories are required for each different part type.
Accordingly, there is still a need in the industry for an apparatus and method to readily and cost-effectively mount components, such as power converter modules, to the bottom of a circuit board. There is further a need to reduce the time and damage issues associated with manual placement and manual soldering. There is still further a need in the art to address the various drawbacks noted above for existing attachment components and manufacturing techniques. There is still a need for a socket physical design that permits attachment to the top side of the board, while allowing for insertion of the power converter module from the bottom side of the board (a “bottom-entry” connection).